Utility interactive inverter with var dispatch capabilities

ABSTRACT

A VAR dispatch system. A central control system connected to a network is configured to receive data reflecting local variations in conditions on a power grid and to transmit system control commands over the network. A plurality of VAR dispatch devices are connected to the network and to the power grid. Each VAR dispatch device is configured to detect local variations in conditions on the power grid and to transmit the data reflecting such local variations to the central control system and to receive control commands from the central control system. Each VAR dispatch device is configured to store power and to output stored power to the power grid based on local variations in conditions on the power grid. Each VAR dispatch device is further configured to output stored power to the power grid when the VAR dispatch device receives system control commands from the central control system.

This application is a continuation of U.S. patent application Ser. No.12/175,314 filed Jul. 17, 2008, now U.S. Pat. No. 9,031,708, whichclaims priority to U.S. Provisional Application Ser. No. 60/950,167entitled “Utility Interactive Inverter with VAR Dispatch Capabilities”filed Jul. 17, 2007, and relates to the subject matter of U.S.Provisional Patent Application Ser. No. 60/878,072 entitled “UtilityConsole for Controlling Aggregated Energy Resources” filed Jan. 3, 2007,which are incorporated herein by reference in their entirety.

This application includes material which is subject to copyrightprotection. The copyright owner has no objection to the facsimilereproduction by anyone of the patent disclosure, as it appears in thePatent and Trademark Office files or records, but otherwise reserves allcopyright rights whatsoever.

FIELD OF THE INVENTION

The present invention relates in general to the field of electric powerdistribution systems, and in particular to methods and systems formeeting periodic increases in demand for electric power.

BACKGROUND OF THE INVENTION

Demand on electric power grids can vary significantly depending onconditions existing at any given time. For example, demand for power mayincrease significantly during a hot summer season due to increased useof air conditioning. During periods of varying demand, voltage ismaintained within the grid by various types of equipment within thegrid, such as voltage regulators and capacitor banks Frequency ismaintained by matching generation with load. When demand exceeds theavailable supply, the utility must either purchase power fromneighboring interconnects or bring additional (possibly less efficient)generation on line.

Bringing resources online to regulate voltage, for example, switching oncapacitor banks, and bringing resources online to supply additionalpower, for example, purchasing power from another source, can be costlyand time consuming. Furthermore, in many cases, monitoring and reactingto voltage instability or generation shortfall must be performedmanually, often at or near the source of the problem, and thus gridmanagement is neither centrally controlled or automated.

OBJECTS AND SUMMARY OF THE INVENTION

Therefore, it is an object of the invention to address the problem ofperiodic power generation shortfalls by sourcing energy to the gridduring periods of high demand when the power system may not have enoughgenerating capacity.

It is a further object of the invention to address the problem ofoutages by providing backup power during an outage by sourcing energy orreactive power to the grid.

It is a further object of the invention to address the problem ofperiodic voltage instability by sourcing reactive power in Volt AmpereReactive units (VAR's) to the grid in order to stabilize voltage in thepower grid.

It is a further object of the invention to provide the above functionson command from a utility (dispatched centrally through system control)or to allow devices within the power grid to react to power systemconditions (such as voltage or frequency) autonomously using advancedalgorithms loaded directly on such devices.

In one embodiment, the invention is a VAR dispatch device. The devicehas a control system connected to a network. The control system isconfigured to receive system control commands over the network from anexternal system. A monitoring device is connected to the control systemand to a power grid. The monitoring device is configured to detect localvariations in conditions on the power grid and communicate the localvariations in conditions on the power grid to the control system. TheVAR dispatch device further includes at least one power storage deviceconnected to the control system and an energy conversion deviceconnected to the control system, the power storage device, and the powergrid. The energy conversion device is configured to input power from thepower storage devices and output the power to the grid varying theproperties of the power.

The control system is further configured to command the power storagedevices and the energy conversion device to output power to the powergrid varying at least one property of the power when the control systemreceives notification of a local variation in conditions on the powergrid. The control system is further configured to command the powerstorage devices and the energy conversion device to output power to thepower grid varying at least one property of the power when the controlsystem receives a system control command from the external systemcommanding the control system to output power to the power grid.

In another embodiment, the invention is a VAR dispatch system. Thesystem has a central control system connected to a network. The controlsystem is configured to receive data reflecting local variations inconditions on a power grid, and is further configured to transmit systemcontrol commands over the network. The VAR dispatch system furtherincludes a plurality of VAR dispatch devices. Each VAR dispatch deviceis connected to the network and to the power grid. Each VAR dispatchdevice is configured to detect local variations in conditions on thepower grid and to transmit the data reflecting local variations inconditions on the power grid to the central control system and toreceive control commands from the central control system. Each VARdispatch device is further configured to store power from at least onesource, and to output stored power to the power grid when localvariations in conditions on the power grid indicate a local state on thepower grid. Each VAR dispatch device is further configured to outputstored power to the power grid when the VAR dispatch device receivessystem control commands from the central control system commanding thedevice to output stored power to the power grid.

In one embodiment, a VAR dispatch device is controlled by a programmablecontrol system connected to an external network. The device has a powerstorage device to store electrical power for dispatch to the power grid.The VAR dispatch device has monitoring hardware to enable the device todetect local variations in conditions on the power grid. The device alsocontains energy conversion hardware to enable the device to output powerfrom the power storage device with varying frequency, voltage, and/orpower factors as conditions demand.

In another embodiment, a number of VAR dispatch devices are combined ina network of devices distributed across a power grid. The devices may beprogrammed to respond autonomously to react to local grid conditions,for example, to stabilize voltage and may also supply a limited quantityof backup power during an outage. The devices may also be controlledcentrally from a central control point. The central control point mayinclude one or more computerized systems which use data acquired fromthe distributed VAR dispatch devices to monitor the operation of thepower grid and which are capable of issuing commands to the VAR dispatchdevices in response to conditions occurring on the grid.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments as illustrated in the accompanyingdrawings, in which reference characters refer to the same partsthroughout the various views. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating principles of theinvention.

FIG. 1 is a block diagram illustrating one embodiment of a VAR dispatchdevice.

FIG. 2 is a schematic of another embodiment of a VAR dispatch devicecontaining a battery and an inverter.

FIG. 3 is a schematic of the closed loop control circuitry of theembodiment shown in FIG. 2.

FIG. 4 is a diagram of an embodiment where multiple VAR dispatch devicesare used across a power grid and centrally controlled.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

The present invention is described below with operational illustrationsof devices and systems for dispatching reactive power to a power grid.It is understood that illustrations may be implemented by means ofanalog or digital hardware and computer program instructions. Thesecomputer program instructions may be provided to a processor of ageneral purpose computer, special purpose computer, ASIC, or otherprogrammable data processing apparatus, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, implements the functions or acts specified inthe illustrations.

FIG. 1 illustrates an embodiment of a VAR dispatch device, 100. Thedevice is connected to a power grid, 200, which may be, for example, thepower grid of a local utility. The VAR dispatch device, 100, iscontrolled by a control system, 110, which may be connected to anexternal network, 300, which can be a wide area network for example, theInternet. The device, 100, has a power storage device, 120, for example,a battery, a capacitor, a fuel cell, or flywheel, to store electricalpower for dispatch to the power grid, 200, on demand. The VAR dispatchdevice has monitoring hardware, 130, to enable the device to detectlocal variations in conditions on the power grid, 200, for example,variations in voltage. Device 100 also contains energy conversionhardware, 140, for example, an inverter, to enable the device to outputpower from the power storage device, 120, to the power grid, 200, withvarying frequency, voltage, and/or power factors as conditions demand.Energy conversion hardware, 140, may also recharge the power storagefrom the power grid.

The control system, 110, of the VAR dispatch device, 100, isprogrammable, and can be programmed to command the device to output ACpower at a specific frequency, voltage, and/or power factor based uponrules downloaded to the device or on specific instruction from anauthorized source. Rules may be downloaded remotely through an externalnetwork, 300, to which the device, 100, is connected.

FIG. 2 illustrates another embodiment of a VAR dispatch device, 400,which includes a battery and an inverter. The inverter, 410, isconstructed using an H bridge (S1, S2, S3 and S4), 412, a seriesinductor (L1), 414, and transformer (Ti), 416. The control system, 420,is a conventional field oriented controller that converts sinusoidalsignals to direct (ID or VD) and quadrature (IQ or VQ) components. A PLL(phase locked loop) synchronizes to the AC line and generates a phasesignal θ. The control system, 420, also includes provision for islanddetection, voltage and frequency range detection. These are safetydevices that disconnect the inverter in the event of a loss of grid. Theanti-island system operates by injecting positive feedback andmonitoring the output voltage of the inverter.

Closed loop control is performed by components in FIG. 3. The measuredvalues are compared to commanded values to generate an error signal thatdrives the modulator, 510, which generates PWM gate signals, 520. The Dquantity controls the real power delivered by the inverter, 410, and theQ quantity controls the reactive power supplied by the inverter. Tooperate the inverter, 410, in backup mode the switch S5, 530, connectsthe modulator, 510, to input the voltage error signal, 540, instead ofthe current error signal, 550.

Referring next to FIG. 4, in another embodiment, a number of VARdispatch devices, 100, may be combined in a network of devicesdistributed across a power grid, 200. Individual devices, 100, arelocated near the load they are intended to support. The devices, 100,may be programmed to respond autonomously to react to local gridconditions, for example, to stabilize voltage. Since the devices, 100,are located near the load they are intended to support, the devices mayalso supply a limited quantity of backup power during an outage.

The devices may also be controlled centrally by, for example, theutility responsible for the power grid, 200, from a central controlpoint, 220. The central control point may include one or morecomputerized systems which use data acquired from the distributed VARdispatch devices, 100, to monitor the operation of the power grid, 200,and which are capable of issuing commands to the VAR dispatch devices.When overall grid conditions become unstable, the control point, 220,could issue commands to one or more VAR dispatch devices to performcertain actions, for example, dispatch power to an area of the grid evenif local grid conditions would not normally trigger the device to do so.Such commands could further specify the rate at which the VAR dispatchdevices should operate. Each VAR dispatch device, 100, can measure andreport conditions of the grid back to central control point, 220, thusforming a monitoring network to a utility SCADA system.

The central control point, 220, can additionally, communicate with, andcontrol, other central control points managing other VAR dispatchdevices. In one embodiment, the central control point communicates withother central control points as if such other central control pointswere VAR dispatch devices.

For example, distributed generation in the form of a rotating machinecould be controlled by a VAR dispatch device and used by the device togenerate additional power on demand. Of course, this would require afuel source, and would have emissions. Alternatively, a renewable oralternative energy source with a static inverter could be used.Typically payback of these systems is, however, very long.

While the invention has been particularly shown and described withreference to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

We claim:
 1. A volt ampere reactive (VAR) dispatch device comprising: acontrol system connected to a network, wherein the control system isconfigured to receive system control commands over the network from anexternal system; a monitoring device operatively connected to thecontrol system and to a power grid, wherein the monitoring device isconfigured to detect local variations in conditions on the power gridand wherein the monitoring device is further configured to communicatethe local variations in conditions on the power grid to the controlsystem; at least one power storage device operatively connected to thecontrol system; an energy conversion device operatively connected to thecontrol system, the power storage device, and the power grid, whereinthe energy conversion device is configured to input power from the atleast one power storage device and output the power to the grid varyingat least one property of the power; wherein the control system isfurther configured to command the at least one power storage device andthe energy conversion device to output the power to the power gridvarying the at least one property of the power when the control systemreceives notification of a local variation in conditions on the powergrid that indicate a state of the power grid; and wherein the controlsystem is further configured to command the at least one power storagedevice and the energy conversion device to output the power to the powergrid varying the at least one property of the power when the controlsystem receives a system control command from the external systemcommanding the control system to output power to the power grid.
 2. TheVAR dispatch device of claim 1 wherein the network is a wide areanetwork and the external system is a central control system of an entitywhich manages the power grid.
 3. The VAR dispatch device of claim 1wherein the control system is further configured to transmit, over thenetwork, the local the variations in conditions on the power gridreceived from the monitoring device to the external system.
 4. The VARdispatch device of claim 1 wherein the at least one property of thepower is selected from the list: frequency, voltage, power factor. 5.The VAR dispatch device of claim 1 wherein the at least one powerstorage device is selected from the list: battery, capacitor, fuel cell,flywheel.
 6. The VAR dispatch device of claim 1 wherein the state of thepower grid is selected from the list: grid instability, insufficientpower on power grid, loss of power on the power grid.
 7. The VARdispatch device of claim 1 wherein the control system is furtherconfigured to command the energy conversion device to recharge at leastone power storage device with power from the power grid.
 8. The VARdispatch device of claim 1 wherein the control system is programmableand is further configured to command the at least one power storagedevice and the energy conversion device to output power to the powergrid with a specific at least one property when a specific state occurson the power grid based on rules downloaded to the control system overthe network from the external system.
 9. The VAR dispatch device ofclaim 1 wherein the energy conversion device is an inverter.
 10. The VARdispatch device of claim 9 wherein the energy conversion device is aninverter comprising an H bridge, a series inductor, and a transformer.11. The VAR dispatch device of claim 9 wherein the inverter furthercomprises a closed loop control configured to compare at least onemeasured value to at least one commanded value to generate an errorsignal, wherein the error signal causes a modulator within the inverterto generate at least one PWM gate signal controlling the power input tothe inverter and the power output by the inverter.
 12. The VAR dispatchdevice of claim 1 wherein the control system is a conventional fieldoriented controller configured to convert sinusoidal signals to directand quadrature components.
 13. The VAR dispatch device of claim 1wherein the control system is further configured for island detection,voltage range detection and frequency range detection.
 14. The VARdispatch device of claim 13 wherein the control system is furtherconfigured to disconnect the energy conversion device from the powergrid if the grid fails.
 15. The VAR dispatch system comprising: acentral control system connected to a network, wherein the controlsystem is configured to receive data reflecting local variations inconditions on a power grid, and wherein the central control system isfurther configured to transmit system control commands over the network;a plurality of VAR dispatch devices, each VAR dispatch device beingconnected to the network and to the power grid; wherein each VARdispatch device is configured to detect local variations in conditionson the power grid and to transmit the data reflecting local variationsin conditions on the power grid to the central control system; whereineach VAR dispatch device is further configured to receive controlcommands from the central control system; wherein each VAR dispatchdevice is further configured to store power from at least one source;wherein each VAR dispatch device is further configured to output storedpower to the power grid when local variations in conditions on the powergrid indicate a local state on the power grid; wherein each VAR dispatchdevice is further configured to output stored power to the power gridwhen the VAR dispatch device receives system control commands from thecentral control system commanding the device to output stored power tothe power grid.
 16. The VAR dispatch system of claim 15 wherein thecentral control system is further configured to use the data reflectinglocal variations in conditions received from the plurality of VARdispatch devices to detect at least one condition on the power grid. 17.The VAR dispatch system of claim 15 is further configured to issuecommands to at least one of the plurality of VAR dispatch devicescommanding the devices to set the rate of response under which the atleast one of the plurality of VAR dispatch devices should operate. 18.The VAR dispatch system of claim 16 wherein the central control systemis further configured, upon detecting the at least one condition on thepower grid, to issue commands to at least one of the plurality of VARdispatch devices commanding the devices to output stored power to thepower grid to mitigate the at least one condition.
 19. The VAR dispatchsystem of claim 15 wherein the local state is selected from the list:grid instability, high demand for power on the grid, insufficient poweron power grid, loss of power on the power grid.
 20. The VAR dispatchsystem of claim 16 wherein the at least one condition is selected fromthe list: grid instability, high demand for power on the grid,insufficient power on power grid, loss of power on the power grid. 21.The VAR dispatch system of claim 15 wherein at least some of theplurality of VAR dispatch devices are each located near a load andsupply backup power to the load during an power grid outage.
 22. The VARdispatch system of claim 15 wherein at least one of the plurality of VARdispatch devices is a second central control system of a second VARdispatch system.
 23. A method of managing a power grid comprising thesteps: receiving, over a network, data reflecting local variations inconditions on a power grid from a plurality of volt ampere reactive(VAR) dispatch devices; determining, using a computer, based on the datareflecting local variations in conditions on the power grid, that atleast one condition that exists on the power grid; transmitting, overthe network, at least one control command to at least one of theplurality of VAR dispatch devices to output power to the power grid tomitigate the at least one condition exists on the power grid.
 24. TheVAR central control system of claim 23 wherein the at least onecondition is selected from the list: grid instability, high demand forpower on the grid, insufficient power on power grid, loss of power onthe power grid.
 25. A volt ampere reactive (VAR) dispatch devicecomprising: a control system connected to a network, wherein the controlsystem is configured to receive system control commands over the networkfrom an external system; a monitoring device operatively connected tothe control system and to a power grid, wherein the monitoring device isconfigured to detect local variations in conditions on the power gridand wherein the monitoring device is further configured to communicatethe local variations in conditions on the power grid to the controlsystem; at least one power storage device operatively connected to thecontrol system; an energy conversion device operatively connected to thecontrol system, the power storage device, and the power grid, whereinthe energy conversion device is configured to input power from the atleast one power storage device and output the power to the grid varyingat least one property of the power; and wherein the control system isfurther configured to command the power storage device and the energyconversion device to output the power to the power grid varying the atleast one property of the power when the control system receives asystem control command from the external system commanding the controlsystem to output power to the power grid.
 26. The volt ampere reactive(VAR) dispatch device of claim 8, wherein the system control commandsfrom the external system are indicative of unstable overall gridconditions and the control system is further configured to command theat least one power storage device and the energy conversion device tooutput the power to the power grid varying the at least one property ofthe power based on the system control command from the external systemeven in cases where the local grid conditions do not trigger the controlsystem to autonomously command the at least one power storage device andthe energy conversion device to output the power to the power gridvarying the at least one property of the power.
 27. The volt amperereactive (VAR) dispatch system of claim 15, wherein the system controlcommands from the central control system are indicative of unstableoverall grid conditions and each VAR dispatch device is furtherconfigured to output stored power to the power grid when the VARdispatch device receives the central control commands from the centralcontrol system commanding the device to output stored power to the powergrid even in cases where local variations in conditions on the powergrid indicate a local state on the power grid do not trigger the VARdispatch device to output stored power to the power grid.
 28. The voltampere reactive (VAR) dispatch system of claim 27, wherein the centralcontrol system is further configured to use data reflecting localvariations in conditions received from the plurality of VAR dispatchdevices to detect the unstable overall grid conditions and to generatethe system control commands to one or more of the plurality of VARdispatch devices.